This application claims the priority of German Patent Application No. 102 05 294.8 filed Feb. 8, 2002. The disclosure of the foregoing priority application and of each and every U.S. and foreign patent and patent application mentioned herein are incorporated herein by reference.
The invention relates to an optoelectronic device for detecting labels having contrasting patterns.
An optoelectronic device is known from German Patent Document DE 198 44 238 A1. The conventional optoelectronic device is used to detect labels, in particular, barcode labels. The optoelectronic device includes a transmitter with a transmitting optic connected downstream of the transmitter, and a receiver with a receiving optic connected in front of the receiver. The light rays emitted by the transmitter and the receiving light rays reflected by the labels are guided over a reflecting unit. The reflecting unit consists of a rotating polygonal mirror wheel with a plurality of mirror surfaces. The reflecting unit periodically guides the light rays emitted by the transmitter over a monitoring range.
Reflecting mirrors, across which the light rays from the transmitted and light rays to the receiver are guided, are arranged between the transmitter and the reflecting unit, as well as between the receiver and the reflecting unit. The reflecting mirrors guide the light rays from the transmitter and the light rays to the receiver over the same mirror surface of the polygonal mirror wheel.
The conventional optoelectronic device includes a plurality of optical components over which the light rays from the transmitter and to the receiver must be guided.
The individual components, in particular the reflecting mirrors, require an exact calibration. This calibration results in an undesirably high assembly expenditure during the manufacture of the optoelectronic device. In addition, the optoelectronic device has an undesirably large structural shape, particularly since the arrangement of the reflecting mirrors and the receiving optic in front of the receiver require a large amount of space.
Another optoelectronic device for detecting barcode labels is known from International publication WO 00/16239. With this optoelectronic device, the transmitter and the receiver are arranged at a distance to each other, one above the other. The light rays emitted by the transmitter and the light rays reflected by the labels are guided over a reflecting unit. The reflecting unit is a polygonal mirror wheel with a plurality of mirror surfaces. The light rays emitted by the transmitter and reflected by the barcodes are respectively guided over the same mirror surface of the polygonal mirror wheel. The light rays from the transmitter and the light rays from the barcodes are guided so as to be spatially separated. Thus, the light rays emitted by the transmitter impinge on the upper partial section of the respective mirror surface on the polygonal mirror wheel while the light rays reflected by the barcodes are guided across the lower partial section a particular mirror surface.
To achieve a complete spatial separation of the light rays from the transmitter and the light rays from the barcodes, the partial sections of the mirror surface must be clearly offset relative to each other.
This conventional optoelectronic device is relatively miniaturized to some degree because the receiver is installed at a distance opposite the reflecting unit, without a receiving optic in front of the receiver. However, as compared to traditional polygonal mirror wheels, the height of the polygonal mirror wheel in the above-described optoelectronic device must be noticeably increased to obtain the desired separation of the light rays. In turn, this requires an undesirable enlargement of the structural shape of the optoelectronic device. A further disadvantage is that the optical axes of the transmitter and the receiver must be aligned precisely, relative to each other and relative to the position of the reflecting unit, to ensure the desired spatial separation of the light rays from the transmitter and the light rays from the barcodes.
It is an object of the invention to design an optoelectronic device for detecting barcodes having the smallest possible structural shape.
The above and other objects are achieved according to an embodiment of an optoelectronic device of the present invention which is set forth herein by way of example only. Exemplary modifications of the invention are additionally described herein.
The optoelectronic device of the present invention detects labels with contrasting patterns. According to an exemplary embodiment, transmitter emits transmitting light rays, and a receiver receives receiving light rays. A reflecting unit is used to guide the light rays from the transmitter periodically inside a monitoring range, and an evaluation unit evaluates the signals output from the receiver. The light rays reflected by the labels are guided via the reflecting unit onto the receiver. The receiver has a light-sensitive surface which at least partially encircles the light rays emitted from the transmitter.
One advantage of the present invention is that the transmitter and the receiver of the optoelectronic device are positioned opposite the reflecting unit, without reflecting mirrors installed in between. According to an exemplary embodiment, as a result of the large-surface, light-sensitive surface that encloses the path of the light rays transmitted by the transmitter, the light rays from the barcodes are guided by the reflecting unit nearly completely onto the receiver, without the aid of a receiving optic. Thus, the optoelectronic device according to the invention has only a small number of optical components and can be produced cheaply with little assembly expenditure. An extremely small structural shape is achieved as a result of directly coordinating the transmitter and the receiver, without the installation of a receiving optic and without the use of reflecting mirrors.
This advantage is further increased in that the light-sensitive surface of the receiver at least partially encloses the light rays emitted by the transmitter, thus resulting in a coaxial guidance of the light rays from the transmitter and the light rays guided to the receiver.
The reflecting unit optionally includes a polygonal mirror wheel with a predetermined number of mirror surfaces. The light rays from the transmitter and the light rays from the barcodes are respectively guided over the same mirror surface of the polygonal mirror wheel.
As a result of the coaxial guidance of the two types light rays, the transmitting light spot projected onto the respective mirror surface is at least partially surrounded by the receiving light spot projected onto the same mirror surface. This results in an efficient use of the mirror surface of the polygonal mirror wheel because it is illuminated almost totally by the two types of light rays. In turn, the dimensions of the mirror surfaces can be adapted optimally to the cross section of the transmitting light spot and the receiving light spot. As a result, the mirror surfaces and thus the complete polygonal mirror wheel have a smaller structural size.
According to an exemplary embodiment, the receiver is arranged on a carrier installed directly downstream of the transmitter. The light-sensitive surface of the receiver and the carrier, however, are each provided with corresponding recesses, and the light rays from the transmitter are guided through the recesses. This type of arrangement for the transmitter and the receiver requires only a small structural volume and the assembly is quick and cost-effective. Moreover, the calibration expenditure is particularly low.
For optical separation of the light rays from the transmitter and the light rays to the receiver and to avoid light rays intended for the receiver from entering the transmitter, the recesses in the carrier and the receiver are fitted with a sleeve, the front end of which optionally projects over the receiver front. The light rays from the transmitter are guided inside this sleeve and have a smaller ray diameter than the inside diameter of the sleeve.
According to one embodiment, the receiver has a one-piece, coherent, light-sensitive surface. It is advantageous if the light-sensitive surface forms a homogeneous, continuous surface that has a high sensitivity for detecting the impinging light rays.
The receiver of another embodiment comprises a number of receiving elements with light-sensitive partial surfaces, which jointly form the light-sensitive surface. Conventional and cost-effective PIN diode elements can be used as receiving elements.